This application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2006-227385 filed in Japan on Aug. 24, 2006, the entire contents of which are hereby incorporated by reference.
The present invention relates to a visual inspection system that assesses the presence of flaws in ceramic balls for use in bearings, ball valves, and the like.
Conventionally, it has commonly been the case with inspection systems for spherical surfaces such as steel balls and the like that the spherical body is generally inspected in air. However, while inspection in air has the advantage of making the spherical body easy to handle, the oil content forms a stain if the spherical surface is not completely degreased by washing, resulting in the spherical body being assessed as defective. Further, the oil content accumulates on the pathway for the balls in the inspection portion, and the adherence of this oil content to the balls may result in a negative assessment. Especially if the spherical body is constructed with an easily corroded metal, there is a possibility of the spherical body rusting when left degreased for a long period of time.
In view of this, the applicant has proposed a system capable of performing surface inspections of a spherical body, without the problem of oil stains such as those described previously, and without the possibility of rusting even with easily corroded metals by making degreasing unnecessary. This system, a main portion of which is shown schematically in FIG. 4, performs surface inspections optically with the spherical body targeted for inspection being immersed in oil. With this surface inspection system, light from a light source 12 is irradiated onto a steel ball 101, being the spherical body targeted for inspection, with the steel ball 101 being immersed in oil and held in place, and the reflected light is received by a light receiving element 13 and converted into electrical signals, after which the presence of flaws in the steel ball 101 is assessed by an assessing portion 11 based on the amount of change in the electrical signals (e.g., see JP 2002-277226A).
However, while optical surface inspection systems that assess the presence of flaws based on the amount of change in electrical signals as described above are ideal for steel balls finished to a mirror surface that are used in common bearings, apparatuses using bearings, ball valves and the like have become faster and more efficient in recent years, and these inspection systems are not effective when it comes to ceramic balls, in demand for their lightness, because even when light is projected the amount of light reflected from a ceramic ball is greatly reduced given that the spherical surface of the ceramic ball is gray or black in color. If the amount of light reflected from the ceramic ball is increased by raising the amount of light from the light source accordingly, the change in signals between flawed and unflawed portions of the spherical surface is reduced because light reflected from objects other than the ceramic ball is also incident on the light receiving element, making it difficult to detect minute flaws. Particularly in the case of ceramic balls, detection was difficult with optical visual inspection systems given the extremely small change in the amount of light reflected from the balls in parts where there were flaws peculiar to ceramics; that is, minute defects such as color unevenness, holes or the like resulting from inclusions in the extreme surface portion. On the other hand, while it is also possible to perform inspections with the naked eye using a microscope, the unavoidable increase in costs due to labor expenses makes this impractical. Also, ceramic balls, unlike steel balls, easily become static electrically charged when friction occurs in the air, attracting small particles of dust in the air, which are viewed as flaws during inspection and lead to erroneous assessments.